Binder for anode for secondary battery, anode for secondary battery including binder, and lithium secondary battery including anode

Abstract

The present invention relates to a binder for an anode for a secondary battery, an anode including the binder, and a secondary battery including the anode. More particularly, the present invention relates to a binder for an anode for a secondary battery that has excellent heat resistance and mechanical properties and an improved binding force because a copolymer is used for the binder, and an anode for a secondary battery. In addition, expansion and shrinkage of the anode may be efficiently suppressed, such that charge and discharge life characteristics and performance of the secondary battery may be improved.

What is claimed is: 
     
       1. A binder for an anode for a secondary battery, comprising: a copolymer having a main chain composed of a repeating unit (A) of the following Formula 1, a repeating unit (B) of the following Formula 2, a repeating unit (C) of the following Formula 3, and a repeating unit (D) of the following Formula 4, 
       
         
           
           
               
               
           
         
         wherein
 R 1  and R 3  are each independently substituted or unsubstituted (C1-C10) hydrocarbyl, 
 R 2  and R 4  are each independently hydrogen or substituted or unsubstituted (C1-C10) hydrocarbyl, 
 M n+  is a cation with an oxidation number of n excluding hydrogen ions, and 
 n is an integer of 1 to 3, and 
 
         wherein a saponification ratio of the copolymer satisfies Expression 1,
   0.55≤saponification ratio=( b+d )/( a+b+c+d )≤0.94  [Expression 1]
 
 wherein a is the number of moles of the repeating unit (A), b is the number of moles of the repeating unit (B), c is the number of moles of the repeating unit (C), and d is the number of moles of the repeating unit (D), 
 wherein (a+b):(c+d) in the copolymer is 5:95 to 95:5, in which a is the number of moles of the repeating unit (A), b is the number of moles of the repeating unit (B), c is the number of moles of the repeating unit (C), and d is the number of moles of the repeating unit (D), 
 wherein a:b in the copolymer is 5:95 to 60:40, in which a is the number of moles of the repeating unit (A) and b is the number of moles of the repeating unit (B), 
 wherein c:d in the copolymer is 5:95 to 50:50, in which c is the number of moles of the repeating unit (C) and d is the number of moles of the repeating unit (D), and 
 wherein a weight average molecular weight of the copolymer is 100,000 to 2,000,000 g/mol. 
 
       
     
     
       2. The binder of  claim 1 , wherein the copolymer is a random copolymer. 
     
     
       3. A composition for an anode for a secondary battery, comprising an anode active material and the binder for an anode for a secondary battery of  claim 1 . 
     
     
       4. The composition of  claim 3 , wherein the anode active material comprises a silicon-based active material. 
     
     
       5. The composition of  claim 4 , wherein the anode active material further comprises a graphite-based active material. 
     
     
       6. The composition of  claim 5 , wherein a mass ratio of the silicon-based active material to the graphite-based active material is 97:3 to 3:97. 
     
     
       7. The composition of  claim 3 , wherein a solid content of the composition is 45 wt % or more. 
     
     
       8. An anode for a secondary battery, comprising a current collector and an anode active material layer disposed on the current collector,
 wherein the anode active material layer is formed of the composition for an anode for a secondary battery of  claim 3 . 
 
     
     
       9. The anode of  claim 8 , wherein a content of the binder in the anode active material layer is 0.5 to 30 wt %. 
     
     
       10. The anode of  claim 8 , wherein a thickness of the anode active material layer is 10 to 120 μm. 
     
     
       11. A secondary battery comprising:
 the anode of  claim 8 ; 
 a cathode; 
 a separator interposed between the anode and the cathode; and 
 an electrolyte. 
 
     
     
       12. The secondary battery of  claim 11 , wherein an expansion rate of the secondary battery is 65% or less. 
     
     
       13. The secondary battery of  claim 11 , wherein a capacity retention rate of the secondary battery after 50 cycles of charging and discharging is 80% or more.